UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS. 


COLLEGE  OF  AGRICULTURE. 

AGRICULTURAL  EXPERIMENT  STATION. 


THE 


CALIFORNIA  PEACH-TREE  BORER. 


By  C.  W.  WOODWORTH. 


"1 


The  Old  Practice  of  Digging  Out  the  Borers. 


BULLETIN  No.  143 

(Berkeley,  September,  1902.) 


SACRAMENTO: 
a.  j.  johnston,   :   :   :   :   :   superintendent  state  printing. 

1902. 


BENJAMIN  IDE  WHEELER,  Ph.D.,  LL.D.,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 

E.  W.  HILGARD,  Ph.D.,  LL.D.,  Director  and  Chemist. 

E.  J.  WICKSON,  M.A.,  Horticulturist,  and  Superintendent  of  Central  Station  Grounds. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Agricultural  Geologist  and  Soil  Physicist.    (Soils  and  Alkali.) 

0.  W.  WOODWORTH,  M.S.,  Entomologist. 

*M.  E.  JAFFA,  M.S.,  Assistant  Chemist.    (Foods,  Fertilizers.) 

G.  W.  SHAW,  M.A.,  Ph.D.,  Assistant  Chemist.    (Soils,  Beet-Sugar.) 

GEORGE  E.  COLBY,  M.S.,  Assistant  Chemist.    (Fruits,  Waters,  Insecticides.) 

LEROY  ANDERSON,  M.S.A.,  Animal  Industries.  San  Luis  Obispo. 

A.  R.  WARD,  B.S.A.,  D.V.M.,  Veterinarian,  Bacteriologist. 

E.  H.  TWIGHT,  B.Sc,  Diploma  E. A.M.,  Viticulturist. 

E.  W.  MAJOR,  B.Agr.,  Dairy  Husbandry. 

A.  V.  STLTBENRAUCH,  M.S.,  Assistant  Horticulturist  and  Superintendent  of  Substations. 

*J.  BURTT  DAVY,  Assistant  Botanist. 

H.  M.  HALL,  M..S.,  Assistant  Botanist. 

W.  T.  CLARKE,  Assistant  Entomologist. 

C.  A.  COLMORE,  B.S.,  Clerk  to  the  Director. 


EMIL  KELLNER,  Foreman  of  Central  Station  Grounds. 
JOHN  TUOHY,  Patron, 


,\ 


.    Tulare  Substation,  Tulare. 
JULIUS  FORRER,  Foreman, 

R.  C.  RUST,  Patron,  ) 

>  Foothill  Substation,  Jackson. 
JOHN  H.  BARBER,  Foreman,  ) 

S.  D.  ME RK,  Patron,  ) 

V  Coast  Range  Substation,  Paso  Robles. 
J.  H.  OOLEY,  Workman  in  charge,  ) 

S.  N.  ANDROUS,  Patron,  )  I  Pomona. 

>-  Southern   California  Substation,   •< 
J.  W.  MTLLS,  Foreman,      )  /Ontario. 

V.  C.  RICHARDS,  Patron,         ) 

)■  Forestry  Station,  Chico. 
T.  L.  BO H LENDER,  in  charge,  ) 

ROY  JONES,  Patron, 

WM.  SHUTT,  Foreman 

*  Absent  on  leave. 


[■  Forestry  Station,  Santa  Monica. 


The  Station  publications  (Reports  and  Bulletins)  will  be  sent  to  any 
citizen  of  the  State  on  application,  so  long  as  available. 


CALIFORNIA  PEACH-TREE  BORER. 


The  most  injurious  insect  in  the  Santa  Clara  Valley  is  generally  con- 
ceded to  be  the  California  peach-tree  borer.  This  insect  is  most  abun- 
dant on  peach  and  apricot  trees,  or  on  prune  trees  growing  on  peach 
and  plum  roots.  It  bores  into  the  bark  just  beneath  the  surface  of  the 
ground,  and  is  most  easily  recognized  by  the  very  characteristic  masses 
of  gum  that  exude  from  the  tree  at  the  point  of  attack.  These  borers 
often  become  so  abundant  as  to  entirely  girdle  large  trees,  causing  their 
death;  and  even  when  not  so  deadly  their  attack  seriously  cripples  the 
tree.  The  labor  necessary  to  dig  out  or  otherwise  destroy  these  insects 
amounts  to  a  great  deal.  This  Station  has  been  repeatedly  called  upon 
to  advise  in  the  matter  of  the  repression  of  this  pest,  and  to  assist  in 
determining  the  facts  involved  in  its  treatment.  Experimental  work 
undertaken  in  response  to  these  inquiries  has  resulted  in  establishing 
some  important  facts,  and  this  bulletin  is  designed  to  furnish  these  data 
and  to  give  a  general  account  of  the  history  of  this  insect,  in  order  that 
growers  may  more  intelligently  direct  their  operations  for  the  suppression 
of  the  pest. 

The  Insect  Peculiar  to  Santa  Clara  Valley. — Very  diligent  inquiry  has 
failed  to  discover  that  the  peach-tree  borer  does  any  serious  injury  in 
any  part  of  the  State  other  than  the  Santa  Clara  Valley.  This  is  partic- 
ularly remarkable  from  the  fact  that  the  Eastern  species  is  so  widespread 
and  so  generally  injurious,  and  from  the  further  fact  that  the  region 
about  San  Jose  has  been  a  distributing  point  for  nursery  stock.  It  is 
from  this  district,  most  probably,  that  the  San  Jose  scale  was  distributed 
over  the  State.  The  insect  is  one  readily  carried  in  nursery  stock,  and 
so  we  must  suppose  that  the  conditions  in  other  parts  of  the  State  must 
be  in  some  particular  unfavorable  to  it,  thus  preventing  its  undue 
increase.  It  is  difficult,  however,  to  conceive  how  the  conditions  in 
this  valley  can  be  so  strikingly  different  from  those  elsewhere  as  to  make 
this  difference  in  the  ability  of  the  insect  to  maintain  itself. 

Significance  Elsewhere. — While  at  the  present  time  the  insect  is  thus 
extremely  local  in  its  distribution,  there  is  every  reason  to  expect  that 
in  time  it  may  suddenly  become  injurious  elsewhere.  The  moth  has 
been  collected  in  many  localities  by  entomologists,  and  probably  occurs 
sparingly  all  over  the  State,  only  awaiting  the  advent  of  the  peculiar 
conditions  which  have  made  it  successful  in  the  struggle  for  existence  in 


4  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

the  Santa  Clara  Valley.  It  is  quite  possible  that  the  insect  has  occurred 
and  has  done  injury  in  other  regions,  and  that  orchardists  have  supposed 
the  death  of  the  affected  trees  to  be  produced  by  other  causes. 

Relatives  of  this  Insect  in  California. — The  California  peach-tree  borer 
belongs  to  the  family  Sesiidae,  a  small  family  of  slender-bodied  moths, 
mostly  day-flying  in  their  habits,  and  often  ornamented  in  a  manner  to 
suggest  a  wasp  in  color  and  shape.  The  species  known  as  occurring  in 
this  State  may  be  distinguished  by  the  following  synopsis : 

SESI.ID.E. 

Tongue  long,  (a);  -rudimentary.  Tibiae  tufted,  Paranthene  ;  -hairy,  Mgeria.  —(a)  Pos- 
terior independent  vein  of  hind  wing  arising  from  posterior  vein,  (6);  -from  center  of 
cross  vein,  Melittia;  -from  end  of  cross  vein.  Palpi  with  long  hairs,  Memythrus ;  -short 
hairs,  Albuna.  —(b)  Tibiae  hairy,  Vespamima;  -slightly  tufted.  $  abdominal  tufts 
narrowing,  9  abdomen  with  lateral  tufts,  Sanninoidea ;  -  $  fanlike,  9  none  lateral. 
Sesia. 

Melittia  gloriosa  feeds  on  sumac. 

Memythrus  robinix  quite  injurious  to  poplars  and  locusts. 

Mgeria.  Abdomen  except  base  yellow,  pacifica;  -banded,  tibialis.  These  insects 
attack  poplars  and  willows. 

Vespamima  sequoix  attacks  pines  and  redwoods. 

Sanninoidea  opalescens  on  peach,  cherry,  apricot,  and  prune.  The  most  injurious 
species  of  the  group  and  the  one  treated  of  in  this  bulletin. 

Albuna  pyramidalis. 

Sesia.  Abdomen  all  blue,  achillx;  -all  black,  albicornis;  -sides,  or  all  of  last  two 
segments  red,  animosa;  -last  three  or  four  red,  behrensii;  -fourth  and  last  two  red, 
polygoni;  -all  banded  white,  candescens;  -all  banded  yellow,  novaroensis ;  -two  white, 
prosopis;  -two  yellow,  neglecta;  -$  with  two  or  three,  9  with  four  yellow,  rutilans; 
-  $  with  four,  9  with  three,  tipuliformis ;  -  $  with  six,  9  with  five  yellow.  Fringe 
red,  rileyana;  -orange,  arizonise. 

The  food  of  only  a  few  of  these  species  has  heen  determined.  The  albicornis  preys 
on  willows ;  tipuliformis  on  currants  and  gooseberries ;  rutilans  on  strawberries ;  and 
prosopis  in  the  galls  on  mesquit. 

Paranthene  palmii,  the  food  of  which  is  unknown. 

LIFE  HISTORY. 

A  good  deal  yet  remains  to  be  learned  in  regard  to  the  life  history  of 
this  insect.  No  one  has  thus  far  made  very  careful  breeding  experiments, 
nor  has  there  been  sufficient  continuous  observation  of  field  conditions, 
to  answer  all  the  questions  that  might  be  raised  in  regard  to  it.  The 
life  history  is  known  to  be  very  different  from  that  of  the  Eastern 
peach-tree  borer,  as  occurring  in  the  Northeastern  States.  It  is  possible, 
however,  that  the  history  of  that  insect  in  the  southern  limit  of  its 
range  might  be  more  like  that  of  our  species,  but  the  knowledge  which 
we  have  of  it  in  the  Southern  States  is  quite  as  meagre  as  of  this  species 
in  California. 

Winter  Condition. — This  insect  is  best  known  in  its  winter  quarters, 
because  it  is  during  the  winter  that  practically  all  of  the  work  for  its 
repression  is  done.  In  striking  contrast  with  the  Eastern  borer,  our 
insect  is  more  or  less  active  all  through  the    winter   season,  and  the 


PEACH-TREE    BORER:    LIFE    HISTORY.  O 

young  worms  grow  and  feed  during  all  the  warmer  weather.  It 
appears  that  pupation  never  occurs  until  well  into  the  spring,  even 
though  the  worm  is  quite  large  in  the  fall.  This  produces  a  tendency 
toward  the  production  of  a  large  spring  brood  of  moths;  but  a  great 
many  of  the  worms  that  are  on  the  tree  in  the  winter  do  not  transform 
until  quite  late  in  the  summer. 

The  larvae  are  found  of  all  sizes  during  the  winter.     Farmers  very 
commonly  suppose  that  this  difference  in  size  represents  distinct  broods, 


Fig.  1.    A  nearly  full-grown  larva  of  the  Peach-tree  Borer.    Magnified  four  diameters. 


Fig.  2.    The  head  from  below.    Still 
more  enlarged. 


Fig.  3.    The  same  from  above. 


and  they  commonly  recognize  three  of  these  sizes,  which  they  designate 
as  the  small,  medium,  and  large  sized  worms.  In  fact,  however,  this 
classification  is  not  sound,  since  every  intergrade  exists  from  the 
smallest  to  the  largest.  During  the  course  of  their  development  these 
insects  molt  like  other  larvae,  each  stage  possessing  a  very  much  larger 
head  than  the  one  immediately  preceding  it.  The  different  stages  can 
usually  be  quite  clearly  distinguished  by  the  size  of  the  head;  but  there 
is  considerable  variation  in  the  size  of  two  insects  in  the  same  stage,  so 
that  we  have  not  been  able  to  satisfy  ourselves  as  to  the  exact  number 


6  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

of  molts.  This  will  have  to  be  determined  by  careful  breeding  experi- 
ments. It  is  not  likely,  however,  that  this  information  will  have  any 
very  significant  economic  bearing  upon  the  problem  of  suppression. 
There  is  a  great  deal  of  difference  between  the  burrow  produced  by  a 
young  worm  as  contrasted  with  that  of  one  of  the  older  individuals,  the 
former  being  always  very  shallow  and  usually  quite  devoid  of  gumming 
material,  whereas  the  burrows  of  the  large  borers  extend  through  the 
bark  and  into  the  solid  wood,  and  are  almost  invariably  indicated  by 
the  mass  of  gum  on  the  outside.  The  time  when  the  burrow  becomes 
gummy,  or  when  the  insect  penetrates  deeply  into  the  bark,  seems  to  be 
wholly  a  matter  of  chance,  or  of  individual  peculiarity. 

The  Gum. — The  most  evident  sign  that  the  worm  is  working  in  the  bark 
of  the  tree  is  the  exudation  of  a  greater  or  less  mass  of  gum  from  the 
burrow.  This  gum  mass  is  so  uniformly  present  that  most  orchardists 
consider  it  an  unfailing  and  only  sign  of  the  work  of  the  insect.  Our 
observations  have  shown  that  this  is  far  from  being  the  case.  A  great 
many  larvae  were  found  by  careful  search,  especially  younger  larvae,  in 
which  there  was  no  evidence  whatever  of  gumming;  and  on  the  other 
hand,  conspicuous  masses  of  gum  occurred  very  commonly  where  there 
was  no  evident  sign  of  insect  work. 

It  appears  to  be  probable  that  the  gum  has  no  necessary  relationship 
to  the  insect  at  all,  but  represents  rather  the  evidence  of  the  work  of 
some  decay-producing  organism  which  has  gained  entrance  to  the  tree 
at  the  point  where  it  was  injured  by  the  feeding  of  the  borer.  Indeed, 
the  presence  of  the  gum  seems  to  be  distasteful  to  the  borers,  sometimes 
it  even  apparently  causes  them  to  abandon  a  burrow  and  start  another. 
Gumming  also  occurs  not  uncommonly  along  the  edges  of  wounds  made 
from  other  causes,  and  almost  always  accompanies  the  attack  of  toad- 
stool fungi  where  it  occurs  along  the  line  separating  the  dead  from  the 
living  bark.  Gumming  may  occur  where  the  insect  attacks  the  tree 
above  the  ground,  but  is  always  more  copious  in  the  moist  situations 
below  the  surface. 

The  fact  that  those  attempting  to  cut  out  the  insect  depend  almost 
wholly  upon  the  presence  of  the  gum  for  the  discovery  of  the  burrows 
of  the  larva,  results  in  worms  being  overlooked  in  case  the  gumming 
has  not  yet  occurred;  or  sometimes  the  tree  may  be  very  seriously 
mutilated  in  endeavoring  to  find  a  worm  corresponding  to  a  mass  of  gum 
which  has  been  produced  by  other  causes. 

The  Burrow. — Ordinarily,  there  seems  to  be  a  great  deal  of  variation 
in  the  shape  and  direction  of  the  burrow — about  as  many  burrowing  up 
as  down.  The  general  direction  of  the  burrow  is  usually  more  nearly 
vertical  than  horizontal,  though  a  few  may  go  directly  around  the  tree. 
Very  careful  study  fails  to  reveal  any  decided  preference  as  to  the  side 


PEACH-TREE    BORER:    LIFE    HISTORY.  I 

of  the  tree  affected,  so  it  would  seem  that  in  all  these  matters  the  location 
or  direction  of  the  burrow  is  simply  an  accident. 

Some  have  supposed  that  there  is  a  certain  definite  arrangement  that 
would  have  to  be  taken  into  consideration  in  the  matter  of  treatment. 
The  habits  of  the  worms  within  the  burrow  are  subject  far  no  recog- 
nized rule.  They  appear  to  move  about  the  burrow,  according  as  the 
needs  of  feeding  or  cleaning-out  compel  them,  with  very  little  regard 
to  temperature  or  time  of  day.  The  burrow  appears  to  be  always  kept 
open  by  the  worm,  and  the  gum  that  gathers  on  the  sides  is  pushed  out 
with  the  excremental  matter  that  accumulates  in  the  burrow.  Some- 
times the  gum  hardens  into  a  tube-like  extension  of  the  burrow,  which 
may  become  as  much  as  an  inch  long. 

This  gum  tube  is  not  to  be  confused  with  the  silken  tube  almost  devoid 
of  gum,  which  is  made  by  the  insect  as  its  transformation  period 
approaches.  The  winter  tube  made  by  the  Eastern  species  seems  to 
resemble  rather  the  transformation  chamber  than  the  gum  tube.  In 
many  cases  the  transformation  chamber  contains  more  or  less  gum  also, 
and  indeed  sometimes  the  tube  is  chiefly  gum  and  excrement  at  one  end, 
and  silk  and  excrement  at  the  other.  Our  species  does  not  appear  to 
have  the  habit  of  making  winter  tubes,  but  continues  to  feed  through 
the  cold  season. 

Spring  Conditions. — With  the  commencement  of  the  flow  of  the  sap 
in  the  spring,  the  older  larvae  proceed  to  the  formation  of  their  trans- 
formation tubes.  These  are  sometimes,  indeed  quite  commonly,  formed 
within  the  burrows,  especially  if  the  amount  of  gum  has  not  been 
excessive.  In  other  cases  they  will  be  upon  the  surface  of  the  bark  at, 
or  near,  the  mouth  of  the  burrow.  At  no  time  of  the  year  can  a  larger 
number  of  worms,  preparing  for  transformation,  be  found  than  in  the 
spring,  due  to  the  fact  evidently  that  many  of  the  wintering  worms 
which  had  for  a  long  while  been  full  grown  and  were  only  deterred  from 
transformation  on  account  of  the  season,  now  suddenly  find  conditions 
favorable  and  proceed  to  prepare  for  their  transformation.  After  the 
tube  is  formed  and  the  insect  ceases  to  feed,  it  still  remains  for  some 
time  in  the  larval  condition,  and  if  disturbed  will  wake  up  at  once; 
indeed,  it  seems  to  be  able  to  reproduce  a  new  tube,  if  removed  from  the 
old  one,  without  any  particular  loss  to  itself.  Finally,  however,  activity 
ceases,  the  insect  somewhat  shrinks  in  size,  and  after  a  short  period  of 
complete  rest,  during  which  it  is  unable  to  walk  if  removed,  the  skin 
breaks  and  discloses  the  pupa  which  has  been  formed  within.  The  life 
of  the  insect  within  the  pupa  does  not  last  very  long,  exactly  how  long 
we  can  not  state,  and  upon  its  conclusion  the  pupa  becomes  suddenly 
active,  pushes  itself  out  of  the  transformation  tube  and  almost  immedi- 
ately gives  forth  the  moth  form.  In  Fig.  4,  showing  the  pupa  of  this 
insect,   will  be   seen   the  structures   which   aid  them  in   this  work  of 


8 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION. 


forcing  the  body  out  of  the  burrow.  The  sharp  edge  appearing  on  the  head 
end  of  the  pupa,  seen  best  in  the  side  view,  enables  the  insect  to  break 
the  structures  ahead  of  it,  and  the  spines  which  bound  the  back  side  of 
most  of  the  abdominal  segments  hold  the  insect  in  place,  or  give  it  a 
point  of  leverage,  so  that  it  can,  by  bending  its  body  back  and  forth, 
gradually  force  its  way  forward.  After  it  has  gotten  into  the  open,  the 
widely  spreading  spines,  shown  at  the  posterior  end  of  the  body,  pre- 
vent further  progress  and  hold  the  pupa  case  to  the  end  of  the  burrow 
during  the  progress  of  the  hatching  of  the  moth.     The  line  of  splitting 


Fig.  4.    Pupa  of  the  Peach-tree  Borer.    Magnified  about  four  times. 


along  the  back,  through  which  the  moth  emerges,  can  be  seen  in  the 
right-hand  figure. 

The  moth  is  not  very  commonly  seen  flying.  Like  the  other  mem- 
bers of  the  family,  it  flies  in  the  daytime  and  not  at  night,  as  is  the 
case  with  most  moths.  It  produces  a  great  many  eggs,  which  are 
laid  upon  the  trunks  of  the  trees  scattered  about,  apparently  with  no 
attempt  at  order.  The  egg  is  beautifully  sculptured,  slightly  flattish, 
but  oval  in  outline.  The  insect  is  quite  prolific,  laying  some  hundreds 
of  eggs,  and  as  they  are,  as  a  rule,  laid  singly,  one  moth  can  injure  an 
immense  number  of  trees.'  Young  worms  on  hatching  from  these  eggs 
enter  some  crack  or  crevice  of  the  bark,  where  they  lie  concealed,  eating 
into  the  substance  of  the  bark,  migrating  about  if  the  situation  is  not 
to  their  liking,  and  usually  travel  downward.  As  a  rule,  they  are  not  sat- 
isfied until  they  get  beneath  the  surface  of  the  ground,  where  they  find 


PEACH-TREE    BORER:    LIFE    HISTORY.  9 

the  bark  still  moist.  If  there  should  be  a  small  amount  of  earth  in  the 
crotch  of  the  tree  they  will  very  often  select  this  place,  and  may  come  to 
full  development  in  the  bark  there.  After  attaining  some  size,  usually 
before  reaching  a  quarter  of  an  inch  in  length,  the  migratory  habit 
seems  to  be  almost  wholly  lost,  and  the  insect  will  thereafter  ordinarily 
complete  its  existence  in  one  burrow.  Throughout  its  life  it  is  active, 
however,  in  keeping  its  burrow  clean,  sometimes  going  quite  out  on  the 
surface  of  the  bark  in  case  the  earth  is  loose,  and  if  removed  from 
the  burrow  will  have  no  trouble  in  establishing  a  new  one. 

Summer  Conditions. — Throughout  the  summer  there  is  a  continuous 
production  of  moths  and  laying  of  eggs,  so  that  at  any  season  of  the 
year  worms  can  be  found  of  nearly  every  size.  The  spring  brood  of 
moths,  however,  which  is,  as  already  explained,  unusually  numerous, 
results  in  there  being  a  size  of  worm  fairly  uniform  and  more  abundant 
in  numbers  than  those  of  any  other  size.  These  worms  become  full 
grown,  or  nearly  full  grown,  by  autumn,  but  do  not  transform  until  the 
following  spring.  Those  individuals  that  are  somewhat  belated  may 
not  be  half  grown  at  the  time  of  the  dropping  of  the  leaves,  but  they 
will  generally  be  ready  for  pupation  by  the  approach  of  spring. 
Sometimes  the  summer  moths  may  in  some  regions  become  more 
abundant  than  usual,  so  as  to  produce  a  fairly  distinct  lot  of  worms  of 
considerably  smaller  size  than  these  spring  larvae.  Occasionally,  also, 
there  may  be  a  similar  abundance  in  the  fall.  These  peculiarities  have 
given  rise  to  the  idea  of  three  broods;  but  it  appears  that  while  there 
may  be  three  times  in  the  year  in  which  the  moth  is  more  abundant 
than  in  others,  and  three  fairly  distinct  sizes  of  larvae,  still  each  lot 
requires  a  full  year  for  its  complete  transformation.  The  summer  and 
fall  broods  do  not  by  any  means  remain  distinct  from  the  spring  brood, 
on  account  of  the  precociousness  of  some  individuals  and  the  belated 
development  of  others,  the  latter  thus  becoming  a  part  of  the  preceding 
or  succeeding  brood.  Commonly,  the  summer  and  fall  broods  can  not  be 
as  clearly  distinguished  as  the  spring  crop  of  moths. 

The  really  significant  part  of  the  outline  of  the  life  history  here  given 
is  that  there  is  no  time  during  the  summer  when  eggs  may  not  be  laid, 
and  that  usually  the  largest  growth  of  young  worms  occurs  early  in  the 
season,  but  that  occasionally  equally  abundant  layings  may  occur  at 
any  time  in  the  summer.  It  will  not  be  possible  under  our  conditions, 
therefore,  to  mark  out  any  plan  of  annual  treatment  which  will  be 
equally  effective  in  different  years. 


10 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


REMEDIES. 

The  remedy,  upon  which  the  most  dependence  is  placed  in  fighting 
the  Eastern  peach-tree  borer,  is  that  of  digging  out  the  worms.  The 
conclusion  of  the  very  elaborate  investigation  by  the  Cornell  Experi- 
ment Station  was  that  this  process  must  form  the  essential  part  of  any 
plan  for  the  control  of  this  insect.  In  addition  to  it,  the  use  of  tar, 
tobacco  stems,  tarred  paper,  or  mounding  with  earth,  must  be  resorted 
to.  The  first  of  these  was  found  to  be  the  most  effective,  but  possibly 
dangerous  to  the  tree  under  some  conditions. 

In  California  all  of  these  methods  and  many  others  have  been  used 
quite  extensively  and  with  more  or  less  satisfactory  results,  but  they  all 
certainly  leave  much  to  be  desired,  since  they  do  not  avoid  the  necessity 
of  also  digging-out.     The  digging-out  process  so  mutilates  the  tree,  even 


Fig.  5.    Two  forms  of  tools  used  in  the  "digging-out"  method. 

when  the  greatest  care  is  exercised,  that  many  growers  are  of  the  opinion 
that  more  injury  is  done  than  when  the  worms  are  left  alone.  When 
the  digging  is  left  to  careless  help,  the  tree  is  often  very  badly  mutilated. 
Fortunately,  the  peach  root  heals  over  a  wound  very  readily  and  is  very 
tenacious  of  life,  often  keeping  the  top  alive  when  there  is  but  a  narrow 
strip  of  bark  left  intact. 

Digging-Out. — The  tools  used  in  digging-out  are  a  shovel,  and  a  pick 
if  the  ground  is  hard,  together  with  a  hoe  or  trowel  for  removing  the 
earth,  and  a  chisel,  gouge,  knife,  or  home-made  tool  for  cutting  out  the 
insect.  Several  forms  of  these  special  tools  are  on  the  market  in  San 
Jose,  two  of  which  are  here  figured.  Some  growers  prefer  a  blacksmith's 
hoof-knife  instead  of  the  form  of  gouge  characteristic  of  these  tools. 


PEACH-TREE    BORER:    REMEDIES.  11 

The  time  of  the  digging-out  is  almost  always  made  a  matter  of  con- 
venience, and  the  facts  we  have  so  far  learned  in  regard  to  the  life 
history  do  not,  as  yet,  prove  that  better  results  would  follow  a  different 
practice.  An  important  feature  of  the  digging-out  method  is  that  it  is 
extremely  difficult  to  find  all,  or  even  the  larger  worms,  in  a  tree;  and 
if  the  worms  are  small  their  discovery  is  almost  or  quite  impossible.  A 
single  going-over  of  the  trees  is  thus  only  partially  effective,  and  many 
orchardists  have  found  that  three  times  during  the  winter  will  not 
exhaust  the  supply,  even  though  it  is  quite  certain  that  no  moths  were 
flying  during  the  intervals.  The  rush  of  other  work  usually  prevents  a 
summer  digging-out  of  the  worms,  though  it  would  seem  that  just  as 
good  or  better  results  might  follow  from  work  at  that  season.  We  do 
not  have  sufficient  data  to  decide  accurately  the  relative  value  of  the 
supplementary  means  used  in  connection  with  the  digging-out  process. 

CARBON    BISULFID. 

A  method  that  has  given  exceedingly  satisfactory  results  under  favor- 
able conditions  is  the  use  of  carbon  bisulfid.  The  fact  that  under  other 
conditions  less  thorough  work  was  done,  and  that  in  some  cases  it  has 
undoubtedly  resulted  in  the  death  of  the  trees,  does  not  signify  that  it 
is  unavailable  for  the  destruction  of  this  pest.  This  substance  has  been 
used  on  a  commercial  scale  only  in  California,  though  the  suggestion 
was  originally  made  for  the  Eastern  borer  by  Prof.  A.  J.  Cook,  Con- 
ductor of  Farmers'  Institutes  for  southern  California,  then  residing  in 
Michigan.  In  Slingerland's  experiments  in  New  York  it  proved  an 
entire  failure,  and  was  condemned  by  him  as  being  too  expensive,  too 
dangerous  to  the  tree,  and  entirely  ineffectual  against  the  insect.  We 
have  no  record  of  the  temperature  or  the  condition  of  the  soil  in  these 
experiments,  and  can  only  conjecture  why  the  results  were  so  unsatis- 
factory. Certainly,  as  used  in  the  orchards  about  San  Jose  there  is 
nothing  as  cheap  as  this  method.  When  properly  handled  the  danger 
to  the  tree  is  none;  and  in  effectiveness,  when  conditions  are  right,  it 
leaves  nothing  to  be  desired. 

Danger  to  the  Tree. — Carbon  bisulfid  has  been  used  for  so  long  a  time  as 
an  insecticide  for  the  control  of  phylloxera  that  we  may  be  very  confident 
as  to  its  uniformity  of  action  and  efficiency  against  insects,  and  also 
of  the  extent  of  the  danger  to  the  plant. 

As  used  against  the  borer  the  danger  from  this  substance  is  wholly 
that  of  the  action  of  the  gas,  since  so  little  liquid  is  applied  to  each  tree 
that  it  all  evaporates  before  it  would  be  possible  for  it  to  penetrate 
through  the  bark  to  the  living  tissue  beneath.  Some  growers  even  make 
it  their  regular  practice  to  pour  the  liquid  on  the  bark,  and  without  bad 
results.  If  enough  material  was  used,  or  the  soil  was  very  wet  so  as  to 
prevent  evaporation,  injury  might  come  from  the  action  of  the  liquid. 


12  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION. 

The  effect  of  the  gas  is  dependent  upon  its  density  and  the  length  of 
time  it  is  acting.  Even  the  most  delicate  growing  parts  of  the  plant 
are  tolerant  of  a  weak  dose  of  gas  continued  almost  indefinitely.  The 
point  at  which  injury  to  root  hairs  occurs  is  very  little  beyond  the 
point  where  it  begins  to  be  effective  against  insects. 

With  the  more  easily  killed  insects  it  might  be  possible  to  use  the 
substance  for  the  complete  eradication  of  a  subterranean  insect,  if  we 
could  obtain  an  even  distribution  of  the  gas  in  the  soil. 

In  actual  practice  it  is  found  that  in  the  case  of  phylloxera  the  use  of 
a  strength  that  will  be  safe  to  the  plant,  almost  always  leaves  some- 
where a  little  colony  of  these  creatures  which  are  able  in  a  short  time 
to  repopulate  the  vine  and  require  another  treatment.  This  repetition, 
every  season  or  two,  is  very  expensive  in  field  work,  so  that  it  pays  only 
in  unusually  valuable  vineyards.  The  chief  uses  of  this  chemical  have 
become,  therefore:  first,  the  stronger  " death  treatment,''  with  which 
both  vines  and  insects  are  destroyed  together;  and,  second,  for  disinfect- 
ing cuttings  or  vines  removed  from  the  soil.  In  the  latter  case  they  are 
given  a  still  stronger  dose,  but  for  a  shorter  period,  and  even  though  the 
smaller  rootlets  may  be  killed,  the  plant  does  not  die,  because  being 
planted  in  new  soil  it  can  replace  any  dead  parts  at  once.  The  bark- 
covered  parts  of  the  plant  are  many  times  more  resistant  to  carbon 
bisulfid  vapor  than  are  the  growing  rootlets  and  root  hairs,  and  these 
latter  are  quite  as  resistant  as  most  insects. 

In  treating  a  peach  tree,  should  there  be  any  root  hairs  immediately 
about  the  crown  they 'might  be  killed  by  the  carbon  bisulfid  at  the 
strength  used,  but  this  would  not  amount  to  anything  to  the  tree.  The 
danger  to  the  tree  would  only  come  from  a  strength  of  gas  and  a  length 
of  time  of  treatment  sufficient  to  injure  the  most  resistant  part  of  the 
root-system. 

The  amount  used  in  any  case  should  not  be  sufficient  to  cause  the 
death  even  of  root  hairs  very  far  away  from  the  trunk;  and  the  real 
danger  to  the  tree  is  not  from  too  great  destruction  of  root  hairs,  but 
from  the  danger  that  the  gas  be  retained  about  the  crown  in  a  concen- 
trated condition  long  enough  to  cause  the  death  of  the  more  resistant 
parts  of  the  tree. 

The  only  thing  that  could  cause  this  retention  of  the  gas  about  the 
crown  is  the  presence  of  water  in  the  soil,  which  closes  up  the  spaces 
between  the  soil  particles,  through  which  the  gas  gradually  diffuses 
itself.  The  danger  is  greatest  in  heavy  soils.  In  a  very  light,  sandy 
or  gravelly  soil  the  difficulty  would  more  likely  be  that  the  soil  might 
be  so  dry  that  the  gas  would  diffuse  so  rapidly  as  to  fail  to  kill  the 
insect;  in  that  case,  of  course,  being  also  perfectly  harmless  to  every 
part  of  the  tree.  Practice  has  shown  that  there  is  a  wide  margin 
between  effectiveness  against  the  insect  and  danger  to  the  bark  of  the 


PEACH-TREE    BORER:    REMEDIES.  13 

tree.     Intelligently  applied,  there  is  no  reason  why  it  might  not  always 
be  entirely  safe  and  effective. 

Condition  of  the  Soil. — The  character  and  condition  of  the  soil  is  the 
most  important  consideration  in  the  use  of  carbon  bisulfid.  The  same 
soil  varies  most  greatly  near  the  surface  in  the  amount  of  moisture  it 
contains,  and  unlike  the  phylloxera  work,  it  is  here  in  this  variable 
surface  soil  that  this  treatment  is  to  be  made. 

Extreme  conditions  should  certainly  be  avoided,  and  uniform  results 
require  uniform  conditions.  The  best  results  have  usually  been  obtained 
in  the  orchards  where  the  soil  was  rather  light  and  in  the  best  condition 
of  tilth.  Under  these  circumstances,  the  method  of  procedure  is  the 
simplest.  All  that  is  necessary  is  to  pour  the  carbon  bisulfid  upon  the 
ground  around  the  tree  close  to  the  trunk  and  immediately  mound  up 
the  earth  a  few  inches  against  the  base  of  the  tree.  In  most  soils  it  will 
be  necessary,  in  order  to  secure  the  best  results,  to  remove  the  soil  that 
immediately  surrounds  the  tree,  as  this  is  somewhat  hard  and  packed, and 
to  replace  it  with  loose  soil  taken  from  the  surface  stirred  by  the  culti- 


Hard  earth  removed.  Filled  with  surface  soil.  Mounded  after  treatment. 

Fig.  6.    Method  of  treatment  in  medium  and  heavy  soils. 

vator.  This  is  made  level  and  the  carbon  bisulfid  applied  as  before,  and 
more  loose  soil  used  in  mounding.  If  the  soil  is  rather  wet  or  heavy  it 
will  be  necessary  to  remove  this  soil  impregnated  with  the  chemical,  so 
as  to  give  the  gas  an  opportunity  to  dissipate  itself  after  a  day  or  two, 
and  thus  prevent  too  long  an  exposure  of  the  root  crown  to  the  gas. 

Except  on  the  lightest  soils  the  earth  should  always  be  removed  if  a 
rain  should  intervene,  as  it  will  effectually  seal  up  the  gas  and  prevent 
its  escape  into  the  air. 

In  some  orchards  sufficiently  dry  soil  may  not  be  found  for  filling  the 
excavations  at  the  time  it  is  desired  to  make  the  treatment,  in  which 
case  chaff  or  straw  may  be  used  instead,  covering  it  well  with  earth-  after 
pouring  on  the  carbon  bisulfid.  This  should,  of  course,  also  be  removed 
after  a  day  or  two. 

In  very  dry,  light  soils,  if  the  carbon  bisulfid  dissipates  itself  too 
rapidly  to  accomplish  the  desired  destruction  of  the  borer,  the  use  of 
water  will  make  it  effective.  For  this  purpose,  excavate  around  the 
trunk,  then  wet  the  soil,  put  back  the  earth,  making  all  level,  apply  the 
carbon  bisulfid,  bank  up  the  earth,  and  sprinkle  the  top  slightly.  In  a 
day  or  two  the  extra  earth  may  be  removed,  if  it  has  not  dried  out 
enough  to  permit  the  escape  of  the  gas. 


14  UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION. 

The  Dose. — In  the  matter  of  the  quantity  to  be  applied  to  a  tree,  there 
is  a  great  deal  of  difference  in  the  practice  of  different  orchardists. 
Economy  would  favor  as  small  a  dose  as  will  be  sufficient,  but  if  too 
small,  nothing  will  be  accomplished  by  the  treatment,  so  orchardists 
generally  feel  that  it  is  better  to  give  too  much  than  too  little.  It  will 
not  be  possible  to  recommend  a  dose  that  will  do  for  all  conditions. 
Probably  a  larger  number  try  to  make  their  average  dose  about  one 
ounce  than  any  other  amount;  and  this  may  be  taken  as  a  tentative 
dose  to  experiment  with.  Each  orchardist  must  determine  for  himself 
that  which  will  be  best  under  his  conditions.  The  most  important 
factor  in  this  matter  is  the  degree  of  looseness  of  the  soil.  The  heavy, 
compact,  moist  soils  require  the  smallest  dose;  and  the  lighter,  looser, 
and  drier  soils  a  larger  quantity  of  the  carbon  bisulfid. 

The  common  practice  is  to  vary  the  dose 
according  to  the  size  of  the  tree,  putting 
often  several  times  as  much  around  a  large 
tree  as  a  small  one.  Some  little  variation 
of  this  kind  should  occur,  but  not  as  much 
as  is  the  practice.  In  an  orchard  with  fairly 
uniform  trees  the  best  practice  would  be  to 
make  the  dose  uniform,  without  regard  to 
the  small  variation  in  the  size  of  the  tree. 
A  little  change  in  the  character  of  the  soil  in 
different  parts  of  the  orchard  is  a  very  much 
more  significant  matter. 

The  method   of  applying   carbon   bisulfid 

Fig.  7.    Can  for  measuring  dose  of    USUally     adopted     is     the     USe     of     a     COmmOD 
carbon  bisulfid.  . 

machine  oil-can.  This  has  the  advantage 
of  convenience,  but  makes  it  difficult  to  apply  a  uniform  dose.  The 
deposition  of  sulfur  in  the  spout  decreases  the  rate  of  flow,  and  often 
gives  trouble  and  makes  the  judging  of  the  size  of  the  amount  dis- 
charged very  difficult.  We  have  planned  a  can  by  which  a  uniform 
dose  can  be  rapidly  measured  and  applied.  It  is  shown  in  Fig.  6.  It 
consists  of  an  ordinary  kerosene  can,  or  a  machine  oiler  could  be 
used  instead.  A  bottle  (a)  with  a  doubly  perforated  cork  and  discharge 
tube  (b)  is  attached  to  the  spout  (c).  The  can  is  reversed  until  the 
bottle-measure  is  filled,  when  by  righting  it  the  liquid  will  pour  out  of 
the  discharge  tube.  A  bottle  of  any  required  size,  fitted  with  perforated 
cork,  can  be  had  at  any  drug  store. 

Summer  Treatment. —  So  far  the  use  of  the  carbon  bisulfid,  like  the 
digging-out  process,  has  been  almost  wholly  confined  to  the  winter 
season.  This  has  been  chiefly  because  this  season  is  the  least  busy, 
and  partly  because  of  the  fear  that  there  would  be  more  danger  to 
the  tree  if  the  chemical  were  applied  when  the  tree  was  not  dormant. 


PEACH-TREE    BORER:    SUMMARY    OF   CONCLUSIONS.  15 

The  danger  to  the  tree  at  this  season  is  not  at  all  greater  than  when 
the  tree  is  dormant,  when  the  treatment  is  made  in  the  manner 
employed  for  this  insect.  The  drier  average  condition  of  the  soil,  which 
favors  the  rapid  diffusion  of  the  gas,  may  cause  some  trouble,  on  account 
of  the  difficulty  of  keeping  the  dose  strong  long  enough  to  kill  the 
insect. 

Quite  as  much,  or  more,  of  the  injury  to  the  trees  is  done  by  the 
worms  during  the  summer  than  during  the  winter,  and  it  would  seem 
desirable  to  make  one  or  more  applications  to  prevent  this  summer 
injury.  As  so  many  of  the  worms  are  small  in  summer,  digging-out 
would  be  very  difficult  to  do  in  a  thorough  manner;  but  carbon  bisulfid 
finds  no  more  difficulty  in  discovering  a  small  worm  than  a  large  one, 
and  the  injury  is  stopped  before  it  is  hardly  begun. 

If  but  a  single  application  is  to  be  made,  the  best  time  to  do  it  is  early 
in  the  winter,  after  all  the  eggs  have  hatched  and  no  more  moths  are 
flying.  The  earlier  worms  will  have  already  done  considerable  injury 
by  this  time,  which  might  be  prevented  by  a  midsummer  treatment. 
Whether  more  treatments  than  these  two  will  be  profitable  in  most 
seasons  it  is  not  possible  now  to  say,  but  careful  observation  of  the  con- 
dition of  the  trees  in  an  orchard  ought  to  enable  any  grower  to  come  to 
satisfactory  conclusions  on  this  subject. 

SUMMARY. 

While  the  peach-tree  borer  is  at  present  injurious  only  in  the  Santa 
Clara  Valley,  a  watch  should  be  kept  for  it  elsewhere. 

As  far  as  known  we  have  but  one  brood  a  year,  but  worms  in  all  con- 
ditions can  be  found  at  almost  any  season,  and  moths  fly  and  lay  eggs 
all  summer. 

The  presence  of  the  gum  can  not  be  depended  upon  as  an  indication 
of  the  young  worm,  so  that  it  is  difficult  to  get  all  when  digging  them 
out. 

Carbon  bisulfid  has  proven  a  most  efficient  method  of  killing  the 
worms. 

The  use  of  carbon  bisulfid  is  not  without  danger  to  the  tree,  but  with 
proper  caution  is  safe. 

The  condition  of  the  soil  is  the  most  important  item  to  consider  in 
the  use  of  carbon  bisulfid. 

The  soil  next  to  the  tree  must  be  loose  enough  to  allow  the  gas  to 
reach  every  part  of  the  crown,  in  order  to  kill  all  the  worms. 

Uniform  treatment  as  to  dose  should  be  attended  to.  The  time  for 
the  most  important  treatment  is  in  the  early  winter.  Probably,  in 
addition,  a  midsummer  treatment  would  be  nearly  as  useful. 


